Zirconium alloys



y 1963 1.. s. RUBENSTEIN ETAL 3,097,094

ZIRCONIUM ALLOYS Filed Sept. 6, 1960 W A D 6 5 750F STEAM I500 PSI 28 DAYS o O o 7 w 5 4 292 226 tam;

14 DAYS .03 .04 .05 WEIGHT 0F SILICON & Frcmcls L. Shubert. BY MTORNZY INVENTORS Lester S. Rubens'rein BSINESSES 0 M AQG United States Patent Pennsylvania Filed Sept. 6, 1960, Ser- No. 54,092

9 Claims. (Cl. 75177) This invention relates to novel zirconium alloys having high resistance to corrosion and good workability.

This application is a continuation-in-part of application Serial No. 843,204, filed September 29, 1959, now abandoned, for Zirconium Alloys.

The low strength of pure zirconium has restricted the use of this material. Much effort has been expended to develop zirconium base alloys having improved strength and high corrosion resistance, and this effort has been successful to a considerable degree. For example, in U.S. Patent No. 2,772,964 of D. E. Thomas et al., issued December 4, 1956, and directed to Zirconium-Base Alloys, there is disclosed a family of workable zirconiumtin-chromium-nickel-iron alloys having good resistance to corrosion and high strength. One of the alloys disclosed therein has found wide commercial acceptance and is presently sold under the name Zircaloy-Z.

The'production, fabrication, and joining of members made from the alloys mentioned in the previous paragraph, often requires slow cooling through the alpha-betaregion. For example, in the bonding process disclosed in copending patent application Serial No. 828,911 of Losco et al., filed July 22, 1959, and directed to Phase Transformation Bonding of Metal Members, the members to be joined are heated to a temperature of about 1,000 C. which produces the beta-phase structure, held at that temperature for a specified period of time, and then furnace-cooled to a temperature of about 400 C, As a result of this furnace cooling the members remain in the alpha-beta region for a period of time suflicient for a partial transformation to the alpha phase. Since the various alloying elements have different solubilities in the alpha and beta phases of zirconium, micro-segregation of these alloying elements will occur on prolonged holding of the members at a temperature in the alphabeta region. The segregation of the alloying elements yvill persist in the body of the members through the subsequent phase transformations which occur in normal processing and use. This segregated condition has been found to give rise to an accelerated rate of corrosion, especially at elevated temperatures in the presence of water or steam.

It is the primary object of this invention to provide for zirconium alloys which may be slowcooled through the alpha-beta region, the alloys characterized by a low corrosion rate at elevated temperatures when in the presence of water or steam, and further characterized in having good hot and cold working properties, such alloys including in predetermined proportion, the elements zirconium, tin, and silicon, and any of iron, nickel, and chromium.

It is another object of this invention to provide zirconium-base alloy members which have been slow cooled through the alpha-beta region characterized by high corrosion resistance when exposed at elevated temperatures to water and steam, the alloy including predeterminedamounts of zirconium, tin, silicon, and one or more of iron, nickel, and chromium.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

Additional information which will assist in the understanding of the invention is presented in the drawing in which the single FlG U R E is a graph of the corrosion re- 3,097,094 Patented July 9, 1963 sistance of several alloys over three test periods in which weight gain is plotted against silicon content.

More specifically, the invention is directed to novel zirconium alloys which may be slow cooled through the alpha'beta region and yet retain high corrosion resistance when exposed to elevated temperatures in the presence of water or steam, and which have good hot and cold working properties, the alloys consisting essentially of from 0.1% to 2.5% by weight of tin, from .015 to 3% silicon, a total of at least 0.1% but not exceeding 2% by weight of at least one metal from period 4 of the periodic table selected from the group consisting of iron, nickel, and chromium, carbon not exceeding .05%, less than 0.5% by weight of incidental impurities, and the balance being zirconium. A somewhat more limited range of tin content; i.e., from .5% to 2.5%, is desirable in some cases.

Good results are also obtained in these alloys when the silicon content'has been in the somewhat narrower range of from .02% to .1%, by weight. However, in the preferred range, in which optimum results are obtained, the silicon addition is from .035 to .045

A zirconium-base alloy in which improved corrosion resistance can be attained by the addition of from .015% to 3% silicon is Within the alloy ranges described above, however, the nickel content is held to a maximum of .O07%.

With such relatively low nickel content, the hydrogen pick-up of the alloy, when exposed to hot water or steam, is greatly reduced. Thus, the adverse effect of absorbed hydrogen on the mechanical strength of members formed from the alloys is avoided. This family of alloys consists'essentially of from 0.5 to 2.5% by weight of tin, from .015 'to .3 silicon, a total of at least 0.1% of at least one metal of period 4 of the periodic table selected from the group consisting of iron, .nickel, and chromium, the nickel not exceeding .007%, and the total weight .of tin, silicon, iron, nickel, and chromium not exceeding 3%, carbon not exceeding .05 the balance being zirconium and less than .5% by weight of incidental impurities. i

While zirconium alloys generally are extremely sensitive to' impurities insofar as corrosion resistance is concerned, we have found that the alloys of our invention will function satisfactorily even when containing relatively large amounts of such impurities as nitrogen, oxygen, and carbon. Nitrogen and carbon, in particular, are known to have deleterious effects on the corrosion resistance of zirconium when it is exposed to water or steam at elevated temperatures. The alloys described herein will tolerate a relatively high percentage of nitrogen and carbon. As much as .0l% nitrogen, and even .025 nitrogen may be present with only slightlyincreased corrosion rates.

It is our particular discovery that additions of silicon, contrary to the general expectation and to some prior experimental evidence, significantly increases the corrosion resistance of the tin-iron-nickel-ohromium-ziroonium alloys. While the mechanism by which silicon accomplishes this desirable result is not fully understood it has been observed that in non-silicon containing alloys agglomerated masses of the segregation product form at grain boundaries, While the silicon-containing alloys the segregation product is uniformly dispersed throughout the alloy and has a peppered appearance. Metallurgically, a uniform dispersion of segregation products is considered to be much more desirable from the standpoint of corrosion resistance than agglomerati'ous of the segregation product at the grain boundaries, and this may be the reason for the improved performance obtained with the alloys of this invention. However, regardless of the reasons, it will be understood that the improvements are obtained by the presence of the silicon.

It should be noted that current specifications for zirconium alloys almost universally specify a maximum of .01% silicon. In accordance with the present invention, it has been found that the effect of silicon in improving the corrosion resistance is significant when silicon is present in an amount of at least about .015 and is more substantial when the silicon is present in an amount of .O2% and more, improving with increasing amounts of up to 0.1% silicon. Improvement in corrosion resistance is also present when silicon ranges from 0.1 to 0.3%. A silicon content in the range from .035 to .045% is pre terred as being highly beneficial from an overall standpoint.

"In preparing the alloy, the zirconium, tin, and the silicon, and iron, nickel, and chromium individually, or any combination of two, or all three, in weight increments, are charged into an arc melting furnace which, for example, may employ a water-cooled copper crucible and a tungsten-tipped electrode. The charge is melted down under an atmosphere of purified argon or helium, or in vacuo, to prevent contamination of the melt. The resulting melt is solidified into an ingot. The ingot may be remelted employing the process set forth in US. application Serial No. 367,524 of Gordon and Hurford, filed July 13, 1953 and directed to Method for Producing Sound and Homogeneous Ingots. The resulting ingot is heated to 1800 =F., and forged into a slab. The zirconium alloy slab is hot rolled at a temperature or 1350 F. or 1550 F. into a sheet or strip or rod which may be employed as desired.

We have obtained particularly satisfactory alloys from the standpoint of low corrosion rate and good Work ability by limiting the total alloying content added to zirconium to a maximum of 3%. For certain critical applications, it has been found desirable to limit the total content of tin, silicon, iron, nickel, and to approximately 2%.

It will be appreciated that other methods of producing the alloy may be employed such, for example, as by initially melting zirconium in an arc melting furnace and then adding pellets prepared by alloying tin, silicon, iron, nickel, and chromium in the desired proportions.

A series of alloys containing varied amounts of silicon was prepared from a base alloy comprising, by weight, 1.5% tin, .0059% silicon, .11 l% iron, 042% nickel, .099% chromium, .0038% nitrogen, and the balance essentially zirconium. In all, four alloys were prepared containing, respectively, 00.59%, .0255%, .0448%, and .0834% or" silicon.

The alloy samples, which had been slow-cooled from the beta phase, were tested in steam at 750 F. for periods up to 56 days, an environment and test period much more severe than usual service requirements for the alloys. From the test results, as plotted in FIG. 1, it will be noted that the alloys having relatively high silicon have improved corrosion resistance as indicated by their lower weight gain for the l4-day, 28-day, and 56-day test periods.

The corrosion product involved in this case is zirconium oxide (ZrO 'Ilhis oxidation product, which is produced when the alloys of this invention are exposed at elevated temperatures to water or steam, forms an adherent lustrous black film on the surface of the test specimen.

The following 14-day, 750 F. steamcorrosion experiment substantiates the efiect or silicon on corrosion resistance in the case of a zirconium alloy member having a relatively high impurity level after a slow cool at the rate of approximately 30 F. per minute from the betaphase region. The weight gain at each silicon level is an average value of six corrosion coupons each from eight different ingots. The alloy tested consisted of from 1.3% to 1.6% by weight of tin, from 07% to .12% by Weight Table I [14 days, 750 F. steam] Wt. Gains, mgjdm.

Average Silicon, Wt. Percent As- Air- Furnace- Reccived Cooled Cooled The above Table I shows the deleterious efiect of slow furnace cooling through the alphabeta range on the zirconium alloy having low silicon content. As between the low silicon alloy in the as-received condition and the same alloy in the furnace-cooled condition, the Weight gain in the latter condition is more than twice the weight gain in the former condition. The table clearly shows that the addition of approxmately 03% silicon reduces the weight gain in the furnace-cooled condition by almost oneahal-f. It also shows the consistently relatively high corrosion resistance of the high silicon alloy regardless of its previous heat treatment.

The tollowing Table II illustrates the beneficial effect of relatively high silicon when nitrogen, which is known to increase the corrosion rate; is present.

Table II [Furnace cooled; 14-day, 75oF. steam] Wt. Gains, mgJdm.

It will be observed from the above table that the presence of approximately .03% silicon tends to reduce the deleterious efiect of relatively high nitrogen.

A further test was conducted which involved subjecting furnace-cooled specimens to 680 F. water for 224 days. These alloy specimens were of the type which included greater than normal amounts of corrosion-promoting impurities such as aluminum, manganese, and copper. The results of the test are presented in Table III.

Table III [Furnace cooled; 224-day, 680 F. Water] Silicon, Wt. percent: Wt. gains, mg./dm. .0044 77.7 .0277 56.3

Again, the presence of silicon in the critical amounts indicated proved beneficial.

In Table IV, which follows, certain physical properties of low-silicon and high-silicon zirconium-base alloys are set [forth for comparison.

Table I V.R00m Temperature Tensile and Hardness Properties (Average) It will be observed from the above table that the highsilicon zirconium alloy has somewhat higher physical properties than the low-silicon zirconium alloy. It is, at any rate, apparent from these data that the addition of silicon does not adversely afiect the physical properties of this zirconium-base alloy.

The lower end of our silicon range is about 0.015% but in the actual alloys of this invention even slightly lower silicon content (but in all events well above 0.010%) is observed from time to time as the result of the metallurgical techniques employed in melting. Some improvement in the corrosion resistant properties for alloys at the low end of the silicon range has been demonstrated.

For example, test samples of an alloy comprising from 1.3% to 1.6% by weight of tin, from :07% to .12% by weight of chromium, from .04% to .08% by weight of nickel, from 109% to .16% by weight of iron, carbon not exceeding .05%, less than .5% by weight of incidental impurities, and the balance zirconium were prepared, including samples with 0.0024% residual silicon and other samples with 0.016% silicon content, and corrosion tests were made in the es-received condition. Typical test results are set forth in Table V:

Table V [3 days, 750 F. steam] Silicon, Weight Wt Gain,

Sample ingJdru.

percent Avg. Weight Range Weight Silicon, Wt.

Gain, mgjdm. Gain, nag/din.

percent Sample (below 0.010)

[14 days, 750 F. steam] Avg. Weight Range Weight Silicon, Wt.

Gain, rug/din. Gain, mgJdm.

percent (below 0.010) 27 25-29 0. 017 25 24 26 0. 017 25 The samples containing silicon in the above table exbibited a corrosion product having a smoother, more uniform, and hence more satisfactory surf-ace than the sample to which no silicon addition was made.

The data presented in Tables V, VI, and VII show that even small amounts of silicon, of the order of 0.015%, will produce significant improvement in the corrosion resistant properties of zirconium alloys.

From the curves presented in FIG. 1, it will be observed that improvement in corrosion resistance generally begins at approximately .02% silicon (and somewhat below this figure under certain conditions) and the improvement is greater as silicon is added in larger amounts approaching .10%. However, particularly striking improvement in the corrosion resistance of these alloys occurs when the silicon content of the alloys amountsto from .035 to .045 This latter amount of silicon will produce an alloy having corrosion resistance approaching the maximum attainable improvement in this property so that larger amounts of silicon result only in slight additional benefits. Consequently the 0.035% to 0.045% silicon is the preferred range.

While the amounts of the various alloying elements have been stated in weight percent in this description, it should be understood that for certain constituents it may sometimes be more convenient to state their quam tity in parts per million (ppm). Thus, for example, the preferred range of silicon content may be stated as from 350 to 450 ppm. Ordinarily, the alloying c011- stituents are stated in weight percent, while impurities, which are often present in much smaller amounts, are stated in parts per million. Where, as here, the alloying constituents are present in such small quantities, either method of stating the amounts is proper.

It will be appreciated that numerous uses may be made of alloys prepared in accordance with the present invention, and that although the present invention has been described with reference to preferred embodiments, it will be apparent to those skilled in the art that variations and modifications in the alloys may be made without departing from the essential spirit and scope of the invention. It is intended to include all such variations and modiiications.

We claim as our invention:

1. An alloy consisting essentially of from 0.1% to 2.5 by weight of tin, from .015% to 30% silicon, and a total of at least .10% but not exceeding approximately 2% by weight of at least one metal from period 4 of the periodic table selected from the group consisting of iron, nickel, and chromium, carbon not exceeding .05 the balance being zirconium and less than .5% by weight of incidental impurities.

2. An alloy consisting essentially of from 0.1% to 2.5% by weight of tin, from .02% to .10% silicon, and a total of at least .10% but not exceeding approximately 2% by weight of at least one metal from period 4 of the periodic table selected from the group consisting of iron, nickel, and chromium carbon not exceeding .05 the balance being zirconium and less than .5% by weight of incidental impurities.

3. An alloy consisting essentially of from .5 to 2.5% by weight of tin, from .015% to 30% silicon, a total of at least .1% of at least one metal of period 4 of the periodic table selected from the group consisting of iron, nickel, and chromium, the total weight of iron, nickel, and chromium not exceeding 2%, carbon not exceeding .05 the balance being zirconium and less than .5% by weight of incidental impurities.

4. An alloy consisting essentially of from .5% to 2.5% by weight of tin, from .015 to .10% silicon, a total of at least .1% of at least one metal of period 4 of the periodic table selected from the group consisting of iron, nickel, and chromium, the nickel not exceeding .007%, and the total weight of tin, silicon, iron, nickel, and chromium not exceeding 3%, carbon not exceeding .05 the balance being zirconium and less than .5% by weight of incidental impurities.

5. An alloy consisting essentially of from .5 to 2.5% by weight of tin, from .02% to 30% silicon, a total of at least .1% of at least one metal of period 4 of the periodic table selected {from the group consisting of iron, nickel, and chromium, the nickel not exceeding .007% and the total weight of tin, silicon, iron, nickel, and chromium not exceeding 3% carbon not exceeding .05% the balance being zirconium and less than .5% by weight of incidental impurities.

6. An alloy consisting of from 1.3% to 1.6% by weight of tin, from .035% to .045% by weight of silicon, from .07% to .12% by weight of chromium, from .04% to .08% by weight of nickel, from .09'% to .16% by weight of iron, carbon not exceeding .05 less than 0.5% by weight of incidental impurities, and the balance being zirconium, the alloy characterized in having superior resistance to corrosion.

7. An alloy consisting of from 1.3%to 1.6% by weight of tin, from .035% to .045 by weight of silicon, from .07% to .12% by weight of chromium, up to .007% by weight of nickel, from .09% to .16% by weight of iron, carbon not exceeding .05 less than 0.5% by Weight of incidental impurities, and the balance being zirconium, the alloy characterized in having superior resistance to corrosion.

8. Members comprising a worked and shaped zirconium base alloy capable of developing high corrosion resistance after slow cooling through the alpha-beta region, the alloy consisting essentially of from .1% to 2.5% by weight of tin, from .02% to .3% by weight of silicon, and a total of at least .1% but not exceeding approximately 2% by Weight of at least one metal trom period 4 of the periodic table selected from the group consisting of iron, nickel, and chromium, carbon not exceeding .05 the balance being zirconium and less than .5% by weight of incidental impurities, the members having high resistance to corrosion in an environment of hot Water or steam at a temperature of 650 F. and hi er.

9. Members comprising a worked and shaped zirconium base alloy which is inherently corrosion resistant after slow cooling through the alpha-beta region, the alloy consisting of from 1.3% to 1.6% by Weight of tin, from 0.35% to .045 by weight of silicon, from .07% to .12% by Weight of chromium, from .04%t0 .08% by weight of nickel, from .09% to .16% by Weight of iron, carbon not exceeding .05%, less than .5% by weight of incidental impurities, and the balance being zirconium, the members exhibiting high resistance to corrosion when exposed to hot water and steam at 650 F. and higher.

No references cited. 

1. AN ALLOY CONSISTING ESSENTIALLY OF FROM 0.1% TO 2.5% BY WEIGHT OF TIN, FROM .015% TO .30% SILICON, AND A TOTAL OF AT LEAST .10% BUT NOT EXCEEDING APPROXIMATELY 2% BY WEIGHT OF AT LEAST ONE METAL FROM PERIOD 4 OF THE PERIODIC TABLE SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL, 